Power Mode Configuration for Touch Sensors

ABSTRACT

In one embodiment, a system includes a touch sensor, measurement circuits, and a monitoring circuit. The measurement circuits are respectively coupled to electrodes of the touch sensor. Each measurement circuit includes a first component, a second component, and a third component. The first component of each measurement circuit is activated in a first power mode and the second and third components of each measurement circuit are deactivated in the first power mode. The monitoring circuit is coupled to the measurement circuits and includes a first component, a second component, and a third component. The monitoring circuit is configured to perform operations in the first power mode. The operations include receiving signals from the measurement circuits and generating an output signal that is proportional to a sum of the signals received from the measurement circuits. A value of the generated output signal indicates whether activity has occurred on the touch sensor.

TECHNICAL FIELD

This disclosure generally relates to touch sensors.

BACKGROUND

According to an example scenario, a touch sensor detects the presenceand position of an object (e.g., a user's finger or a stylus) within atouch-sensitive area of touch sensor array overlaid on a display screen,for example. In a touch-sensitive-display application, a touch sensorarray allows a user to interact directly with what is displayed on thescreen, rather than indirectly with a mouse or touch pad. A touch sensormay be attached to or provided as part of a desktop computer, laptopcomputer, tablet computer, personal digital assistant (PDA), smartphone,satellite navigation device, portable media player, portable gameconsole, kiosk computer, point-of-sale device, or other device. Acontrol panel on a household or other appliance may include a touchsensor.

There are a number of different types of touch sensors, such as forexample resistive touch sensors, surface acoustic wave touch sensors,and capacitive touch sensors. In one example, when an object physicallytouches a touch screen within a touch sensitive area of a touch sensorof the touch screen (e.g., by physically touching a cover layeroverlaying a touch sensor array of the touch sensor) or comes within adetection distance of the touch sensor (e.g., by hovering above thecover layer overlaying the touch sensor array of the touch sensor), achange in capacitance may occur within the touch screen at a position ofthe touch sensor of the touch screen that corresponds to the position ofthe object within the touch sensitive area of the touch sensor. A touchsensor controller processes the change in capacitance to determine theposition of the change of capacitance within the touch sensor (e.g.,within a touch sensor array of the touch sensor).

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and itsadvantages, reference is made to the following descriptions, taken inconjunction with the accompanying drawings, in which:

FIG. 1 illustrates an example system that includes a touch sensor,according to an embodiment of the present disclosure;

FIG. 2 illustrates an example electrode pattern of electrodes of a touchsensor array, according to an embodiment of the present disclosure;

FIG. 3 illustrates an example system for a power mode configuration fora touch sensor, according to an embodiment of the present disclosure;and

FIG. 4 illustrates an example method for configuring a power mode for atouch sensor, according to an embodiment of the present disclosure.

DESCRIPTION OF EXAMPLE EMBODIMENTS

Devices that include touch sensors often spend significant time in astate in which the touch sensor is unused. For example, a user may placethe device in a stand-by mode, or sleep mode, in which in an embodiment,a display of the device is turned off and the touch sensor of the deviceis not actively detecting the presence of an object or is detecting thepresence of an object on a reduce basis relative to when the device isfully powered. As another example, the device may be in use for somebackground application (e.g., playing music), but the touch sensor ofthe device may go unused while that background application is operating.When the device is in a stand-by mode or the touch sensor is otherwiseunused, for example, it may be desirable to conserve power that wouldotherwise be consumed by the touch sensor and other components.Detecting when to power on the touch sensor (e.g., a touch sensorcontroller of the touch sensor) can introduce power-consuming activitiesand present additional problems.

An embodiment of the present disclosure provides an idle power mode fora touch sensor. In idle power mode, the power consumption of operatingthe touch sensor is reduced, in response to the touch sensor detectinglimited activity on the touch screen for example. In the idle powermode, the touch sensor may detect the occurrence of a potential touchbut may omit processing to detect a location of a touch, the number oftouches, or the nature of the touch (e.g., finger, glove, stylus).Reducing the power consumption of operating a touch sensor during idlepower mode may include deactivating (i.e., powering off) certaincomponents of each measurement circuit (which may also be referred to asa slice) of the touch sensor and determining whether activity hasoccurred based on a sum of the signals received from each of themeasurement circuits, as described below. As a particular example,embodiments of the present disclosure use a monitoring circuit toreceive signals from an amplifier of each of the measurement circuitswhile an integrator and an analog-to-digital converter (“ADC”) of eachof the measurement circuits are deactivated. The monitoring circuitgenerates an output signal proportional to a sum of the signals receivedfrom the measurement circuits, and the generated output signal indicateswhether some activity has occurred on the touch sensor.

In one embodiment, a system includes a touch sensor, a plurality ofmeasurement circuits, and a monitoring circuit. The touch sensorincludes a plurality of electrodes. The plurality of measurementcircuits are respectively coupled to the plurality of electrodes of thetouch sensor, wherein each measurement circuit includes a firstcomponent, a second component, and a third component. The firstcomponent of each measurement circuit is activated in a first power modeand the second component and the third component of each measurementcircuit are deactivated in the first power mode. The monitoring circuitis coupled to the first component of each measurement circuit. Themonitoring circuit includes a first component, a second component, and athird component. The first component, the second component, and thethird component of the monitoring circuit are activated in the firstpower mode. The monitoring circuit performs operations in the firstpower mode, which include receiving respective signals from theplurality of measurement circuits and generating an output signal thatis proportional to a sum of the signals received from the plurality ofmeasurement circuits. A value of the generated output signal indicateswhether activity has occurred on the touch sensor.

FIG. 1 illustrates an example system 100 that includes a touch sensor102, according to an embodiment of the present disclosure. Touch sensor102 includes a touch sensor array 106 and a touch sensor controller 108.Touch sensor array 106 and touch sensor controller 108 detect thepresence and position of a touch or the proximity of an object within atouch-sensitive area of touch sensor array 106.

Touch sensor array 106 includes one or more touch-sensitive areas. Inone embodiment, touch sensor array 106 includes an array of electrodesdisposed on one or more substrates, which may be made of a dielectricmaterial. Reference to a touch sensor array may encompass both theelectrodes of touch sensor array 106 and the substrate(s) on which theyare disposed. Alternatively, reference to a touch sensor array mayencompass the electrodes of touch sensor array 106, but not thesubstrate(s) on which they are disposed.

In one embodiment, an electrode is an area of conductive materialforming a shape, such as for example a disc, square, rectangle, thinline, other shape, or a combination of these shapes. One or more cuts inone or more layers of conductive material may (at least in part) createthe shape of an electrode, and the area of the shape may (at least inpart) be bounded by those cuts. In one embodiment, the conductivematerial of an electrode occupies approximately 100% of the area of itsshape. For example, an electrode may be made of indium tin oxide (ITO)and the ITO of the electrode may occupy approximately 100% of the areaof its shape (sometimes referred to as 100% fill). In one embodiment,the conductive material of an electrode occupies less than 100% of thearea of its shape. For example, an electrode may be made of fine linesof metal or other conductive material (FLM), such as for example copper,silver, or a copper- or silver-based material, and the fine lines ofconductive material may occupy approximately 5% of the area of its shapein a hatched, mesh, or other pattern. Reference to FLM encompasses suchmaterial. Although this disclosure describes or illustrates particularelectrodes made of particular conductive material forming particularshapes with particular fill percentages having particular patterns, thisdisclosure contemplates, in any combination, electrodes made of otherconductive materials forming other shapes with other fill percentageshaving other patterns.

The shapes of the electrodes (or other elements) of a touch sensor array106 constitute, in whole or in part, one or more macro-features of touchsensor array 106. One or more characteristics of the implementation ofthose shapes (such as, for example, the conductive materials, fills, orpatterns within the shapes) constitute in whole or in part one or moremicro-features of touch sensor array 106. One or more macro-features oftouch sensor array 106 may determine one or more characteristics of itsfunctionality, and one or more micro-features of touch sensor array 106may determine one or more optical features of touch sensor array 106,such as transmittance, refraction, or reflection.

Although this disclosure describes a number of example electrodes, thepresent disclosure is not limited to these example electrodes and otherelectrodes may be implemented. Additionally, although this disclosuredescribes a number of example embodiments that include particularconfigurations of particular electrodes forming particular nodes, thepresent disclosure is not limited to these example embodiments and otherconfigurations may be implemented. In one embodiment, a number ofelectrodes are disposed on the same or different surfaces of the samesubstrate. Additionally or alternatively, different electrodes may bedisposed on different substrates. Although this disclosure describes anumber of example embodiments that include particular electrodesarranged in specific, example patterns, the present disclosure is notlimited to these example patterns and other electrode patterns may beimplemented.

A mechanical stack contains the substrate (or multiple substrates) andthe conductive material forming the electrodes of touch sensor array106. For example, the mechanical stack may include a first layer ofoptically clear adhesive (OCA) beneath a cover panel. The cover panelmay be clear and made of a resilient material for repeated touching,such as for example glass, polycarbonate, or poly(methyl methacrylate)(PMMA). This disclosure contemplates the cover panel being made of anymaterial. The first layer of OCA may be disposed between the cover paneland the substrate with the conductive material forming the electrodes.The mechanical stack may also include a second layer of OCA and adielectric layer (which may be made of PET or another material, similarto the substrate with the conductive material forming the electrodes).As an alternative, a thin coating of a dielectric material may beapplied instead of the second layer of OCA and the dielectric layer. Thesecond layer of OCA may be disposed between the substrate with theconductive material making up the electrodes and the dielectric layer,and the dielectric layer may be disposed between the second layer of OCAand an air gap to a display of a device including touch sensor array 106and touch sensor controller 108. For example, the cover panel may have athickness of approximately 1 millimeter (mm); the first layer of OCA mayhave a thickness of approximately 0.05 mm; the substrate with theconductive material forming the electrodes may have a thickness ofapproximately 0.05 mm; the second layer of OCA may have a thickness ofapproximately 0.05 mm; and the dielectric layer may have a thickness ofapproximately 0.05 mm.

Although this disclosure describes a particular mechanical stack with aparticular number of particular layers made of particular materials andhaving particular thicknesses, this disclosure contemplates othermechanical stacks with any number of layers made of any materials andhaving any thicknesses. For example, in one embodiment, a layer ofadhesive or dielectric may replace the dielectric layer, second layer ofOCA, and air gap described above, with there being no air gap in thedisplay.

One or more portions of the substrate of touch sensor array 106 may bemade of polyethylene terephthalate (PET) or another material. Thisdisclosure contemplates any substrate with portions made of anymaterial(s). In one embodiment, one or more electrodes in touch sensorarray 106 are made of ITO in whole or in part. Additionally oralternatively, one or more electrodes in touch sensor array 106 are madeof fine lines of metal or other conductive material. For example, one ormore portions of the conductive material may be copper or copper-basedand have a thickness of approximately 5 microns (μm) or less and a widthof approximately 10 μm or less. As another example, one or more portionsof the conductive material may be silver or silver-based and similarlyhave a thickness of approximately 5 μm or less and a width ofapproximately 10 μm or less. This disclosure contemplates any electrodesmade of any materials.

In one embodiment, touch sensor array 106 implements a capacitive formof touch sensing. In a mutual-capacitance implementation, touch sensorarray 106 may include an array of drive and sense electrodes forming anarray of capacitive nodes. A drive electrode and a sense electrode mayform a capacitive node. The drive and sense electrodes forming thecapacitive node are positioned near each other but do not makeelectrical contact with each other. Instead, in response to a signalbeing applied to the drive electrodes for example, the drive and senseelectrodes capacitively couple to each other across a space betweenthem. A pulsed or alternating voltage applied to the drive electrode (bytouch sensor controller 108) induces a charge on the sense electrode,and the amount of charge induced is susceptible to external influence(such as a touch or the proximity of an object). When an object touchesor comes within proximity of the capacitive node, a change incapacitance may occur at the capacitive node and touch sensor controller108 measures the change in capacitance. By measuring changes incapacitance throughout the array, touch sensor controller 108 determinesthe position of the touch or proximity within touch-sensitive areas oftouch sensor array 106.

In a self-capacitance implementation, touch sensor array 106 may includean array of electrodes of a single type that may each form a capacitivenode. When an object touches or comes within proximity of the capacitivenode, a change in self-capacitance may occur at the capacitive node andtouch sensor controller 108 measures the change in capacitance, forexample, as a change in the amount of charge implemented to raise thevoltage at the capacitive node by a predetermined amount. As with amutual-capacitance implementation, by measuring changes in capacitancethroughout the array, touch sensor controller 108 determines theposition of the touch or proximity within touch-sensitive areas of touchsensor array 106. This disclosure contemplates any form of capacitivetouch sensing.

In one embodiment, one or more drive electrodes together form a driveline running horizontally or vertically or in other orientations.Similarly, in one embodiment, one or more sense electrodes together forma sense line running horizontally or vertically or in otherorientations. As one particular example, drive lines run substantiallyperpendicular to the sense lines. Reference to a drive line mayencompass one or more drive electrodes making up the drive line, andvice versa. Reference to a sense line may encompass one or more senseelectrodes making up the sense line, and vice versa.

In one embodiment, touch sensor array 106 includes drive and senseelectrodes disposed in a pattern on one side of a single substrate. Insuch a configuration, a pair of drive and sense electrodes capacitivelycoupled to each other across a space between them form a capacitivenode. As an example self-capacitance implementation, electrodes of asingle type are disposed in a pattern on a single substrate. In additionor as an alternative to having drive and sense electrodes disposed in apattern on one side of a single substrate, touch sensor array 106 mayhave drive electrodes disposed in a pattern on one side of a substrateand sense electrodes disposed in a pattern on another side of thesubstrate. Moreover, touch sensor array 106 may have drive electrodesdisposed in a pattern on one side of one substrate and sense electrodesdisposed in a pattern on one side of another substrate. In suchconfigurations, an intersection of a drive electrode and a senseelectrode forms a capacitive node. Such an intersection may be aposition where the drive electrode and the sense electrode “cross” orcome nearest each other in their respective planes. The drive and senseelectrodes do not make electrical contact with each other—instead theyare capacitively coupled to each other across a dielectric at theintersection. Although this disclosure describes particularconfigurations of particular electrodes forming particular nodes, thisdisclosure contemplates other configurations of electrodes formingnodes. Moreover, this disclosure contemplates other electrodes disposedon any number of substrates in any patterns.

As described above, a change in capacitance at a capacitive node oftouch sensor array 106 may indicate a touch or proximity input at theposition of the capacitive node. Touch sensor controller 108 detects andprocesses the change in capacitance to determine the presence andposition of the touch or proximity input. In one embodiment, touchsensor controller 108 then communicates information about the touch orproximity input to one or more other components (such as one or morecentral processing units (CPUs)) of a device that includes touch sensorarray 106 and touch sensor controller 108, which may respond to thetouch or proximity input by initiating a function of the device (or anapplication running on the device). Although this disclosure describes aparticular touch sensor controller 108 having particular functionalitywith respect to a particular device and a particular touch sensor 102,this disclosure contemplates other touch sensor controllers having anyfunctionality with respect to any device and any touch sensor.

In one embodiment, touch sensor controller 108 is implemented as one ormore integrated circuits (ICs), such as for example general-purposemicroprocessors, microcontrollers, programmable logic devices or arrays,application-specific ICs (ASICs). Touch sensor controller 108 comprisesany combination of analog circuitry, digital logic, and digitalnon-volatile memory. In one embodiment, touch sensor controller 108 isdisposed on a flexible printed circuit (FPC) bonded to the substrate oftouch sensor array 106, as described below. The FPC may be active orpassive. In one embodiment, multiple touch sensor controllers 108 aredisposed on the FPC.

In an example implementation, touch sensor controller 108 includes aprocessor unit, a drive unit, a sense unit, and a storage unit. In suchan implementation, the drive unit supplies drive signals to the driveelectrodes of touch sensor array 106, and the sense unit senses chargeat the capacitive nodes of touch sensor array 106 and providesmeasurement signals to the processor unit representing capacitances atthe capacitive nodes. The processor unit controls the supply of drivesignals to the drive electrodes by the drive unit and processesmeasurement signals from the sense unit to detect and process thepresence and position of a touch or proximity input withintouch-sensitive areas of touch sensor array 106. The processor unit mayalso track changes in the position of a touch or proximity input withintouch-sensitive areas of touch sensor array 106. The storage unit storesprogramming for execution by the processor unit, including programmingfor controlling the drive unit to supply drive signals to the driveelectrodes, programming for processing measurement signals from thesense unit, and other programming. Although this disclosure describes aparticular touch sensor controller 108 having a particularimplementation with particular components, this disclosure contemplatestouch sensor controller having other implementations with othercomponents.

Tracks 110 of conductive material disposed on the substrate of touchsensor array 106 couple the drive or sense electrodes of touch sensorarray 106 to connection pads 112, also disposed on the substrate oftouch sensor array 106. As described below, connection pads 112facilitate coupling of tracks 110 to touch sensor controller 108. Tracks110 may extend into or around (e.g., at the edges of) touch-sensitiveareas of touch sensor array 106. In one embodiment, particular tracks110 provide drive connections for coupling touch sensor controller 108to drive electrodes of touch sensor array 106, through which the driveunit of touch sensor controller 108 supplies drive signals to the driveelectrodes, and other tracks 110 provide sense connections for couplingtouch sensor controller 108 to sense electrodes of touch sensor array106, through which the sense unit of touch sensor controller 108 sensescharge at the capacitive nodes of touch sensor array 106.

Tracks 110 are made of fine lines of metal or other conductive material.For example, the conductive material of tracks 110 may be copper orcopper-based and have a width of approximately 100 μm or less. Asanother example, the conductive material of tracks 110 may be silver orsilver-based and have a width of approximately 100 μm or less. In oneembodiment, tracks 110 are made of ITO in whole or in part in additionor as an alternative to the fine lines of metal or other conductivematerial. Although this disclosure describes particular tracks made ofparticular materials with particular widths, this disclosurecontemplates tracks made of other materials and/or other widths. Inaddition to tracks 110, touch-sensor array 106 may include one or moreground lines terminating at a ground connector (which may be aconnection pad 112) at an edge of the substrate of touch sensor array106 (similar to tracks 110).

Connection pads 112 may be located along one or more edges of thesubstrate, outside a touch-sensitive area of touch sensor array 106. Asdescribed above, touch sensor controller 108 may be on an FPC.Connection pads 112 may be made of the same material as tracks 110 andmay be bonded to the FPC using an anisotropic conductive film (ACF). Inone embodiment, connection 114 includes conductive lines on the FPCcoupling touch sensor controller 108 to connection pads 112, in turncoupling touch sensor controller 108 to tracks 110 and to the drive orsense electrodes of touch sensor array 106. In another embodiment,connection pads 112 are connected to an electro-mechanical connector(such as, for example, a zero insertion force wire-to-board connector).Connection 114 may or may not include an FPC. This disclosurecontemplates any connection 114 between touch sensor controller 108 andtouch sensor array 106.

FIG. 2 illustrates in plan view an example electrode pattern ofelectrodes 210 and 220 of touch sensor array 200, according to anembodiment of the present disclosure. In one example, touch sensor array200 corresponds to touch sensor array 106, described above withreference to FIG. 1. Electrodes 210 of touch sensor array 200 areoriented in a first direction and electrodes 220 are oriented in asecond direction different from the first direction, such that thetouch-sensitive area of touch sensor array 200 is defined by thetwo-dimensional array of electrodes 210 and electrodes 220. In theillustrated example, the first direction and the second direction areperpendicular to each other. Electrodes 210 and electrodes 220 may bedescribed based on their orientation in touch sensor array 200. Forexample, electrodes oriented along a horizontal direction (electrodes210 a-q in the illustrated example) may be referred to as x-electrodesand electrodes oriented along a vertical direction (electrodes 220 a-iin the illustrated example) may be referred to as y-electrodes. Asanother example, electrodes oriented along a horizontal direction(electrodes 210 a-q in the illustrated example) may be referred to asx-lines and electrodes oriented along a vertical direction (electrodes220 a-i in the illustrated example) may be referred to as y-lines.

Electrodes 210 and electrodes 220 overlap at points along theelectrodes. In a mutual capacitive mode of operation, capacitive nodesare formed at areas where electrodes 210 and 220 overlap when theelectrodes in a first direction (e.g., electrodes 210) operate as driveelectrodes and the electrodes in a second direction (e.g., electrodes220) operate as sense electrodes and when a drive signal is applied tothe electrodes operating as drive electrodes.

In one embodiment, electrodes 210 and electrodes 220 are disposed on thesame side of a substrate. In such embodiments, to ensure that electrodes210 and electrodes 220 are electrically isolated from one another,electrodes 210 and electrodes 220 are separated by a dielectric or othermaterial at points where electrodes 210 and electrodes 220 overlap. Incertain other embodiments, electrodes 210 and electrodes 220 aredisposed on opposing sides of a substrate, the substrate being made of adielectric or other material that electrically isolates electrodes 210and electrodes 220 from one another. In certain other embodiments,electrodes 210 and electrodes 220 are disposed on respective surfaces ofdifferent substrates, which are positioned with respect to each othersuch that electrodes 210 and electrodes 220 are electrically isolatedfrom each other at points where electrodes 210 and electrodes 220overlap. For example, one or more of the substrates may be positionedbetween electrodes 210 (positioned on one of the substrates) andelectrodes 220 (positioned on the other of the substrates) or anadditional substrate, such as a dielectric substrate, or air gap issandwiched between the two substrates on which electrodes 210 andelectrodes 2220 are formed.

In a self-capacitance configuration, electrodes 210 and electrodes 220of touch sensor array 200 may operate as a single type such that theyeach form a capacitive node. Although this disclosure describes touchsensor array 200 having particular configurations of particularelectrodes, this disclosure contemplates other configurations ofelectrodes. For example, electrodes 210 of touch sensor array 200 mayoperate as sense electrodes and electrodes 220 of touch sensor array 200may operate as drive electrodes.

It should be understood that FIG. 2 illustrates just one example touchsensor array 200 that may be used according to certain embodiments ofthe present disclosure. The present disclosure contemplates using othertypes of touch sensor arrays, which may have different configurationsand types of operation.

FIG. 3 illustrates an example system 300 for a power mode configurationfor a touch sensor 302, according to an embodiment of the presentdisclosure. In one example, system 300 corresponds to system 100 andtouch sensor 302 corresponds to touch sensor 102, described above withreference to FIG. 1.

Touch sensor controller 108, and thereby touch sensor 102, may operatein a variety of power modes. In an embodiment, a power mode reflects oneor more of the amount of power consumed by one or more components of adevice housing touch sensor 102, an amount of power provided to one ormore components of a device housing touch sensor 102, and the componentsof the device housing touch sensor 102 to which power is provided.

As a first example of a power mode, touch sensor controller 108 may attimes operate in a first power mode, which may be referred to as an idlepower mode. In one embodiment, an idle power mode of touch sensorcontroller 108 includes, either exclusively or non-exclusively, whencertain touch scanning operations of touch sensor controller 108 arepowered down. As an example, one or more components (e.g., integrators326 a-n and ADCs 328 a-n of measurement circuits 320 a-n) of touchsensor 302 may be powered down in idle power mode. In such an example,touch sensor controller 108 may be in a state where it receives powerfor scanning touch sensor array 106 for detecting some activity but doesnot receive power for scanning of touch sensor array 106 to detect thelocation of the activity or the nature of the activity. Detecting someactivity may include detecting a potential touch, such as the presenceof an object (e.g., a finger or a stylus), on or a device. In certainembodiments, idle power mode differs from a deep sleep power mode. Indeep sleep power mode, touch sensor 102 is not required to sense touchsensor array 106 for activity. While an example idle power mode in whichcertain touch scanning operations are powered down has been described,the present disclosure contemplates different and or additionaloperations of touch sensor 102 being powered down in the idle powermode.

Touch sensor 102 may enter this idle power mode in a variety ofsituations. For example, touch sensor 102 may enter idle power mode whena device that houses touch sensor 102 enters a standby mode. As anotherexample, touch sensor 102 may enter idle power mode when touch sensor102 has not detected the presence of an object (e.g., a finger or astylus contacting or otherwise within a detectable range of touch sensor102) for some predetermined period of time. This situation could beencountered, for example, if the device that houses touch sensor 102 isbeing used for some background application (e.g., playing music) but theuser of the device is otherwise not interacting with touch sensor 102 ofdevice 200.

As a second example of a power mode, a second power mode may refer to anactive power mode in which power is provided to touch sensor 102 (e.g.,to touch sensor controller 108) for determining spatial information(e.g., a location of one or more touches and/or the number of touches)and/or touch classification information (e.g., whether the nature of thetouch is a finger, glove, or stylus). As an example, integrators 326 a-nand ADCs 328 a-n of measurement circuits 320 a-n of touch sensor 302 maybe powered on in active power mode.

System 300 of FIG. 3 may be used by one or more devices to improve theidle power consumption of the device. A device is any personal digitalassistant, cellular telephone, smartphone, tablet computer, automaticteller machines (ATMs), home appliances, personal computers, and anyother device having a touch screen. In the illustrated example,components of system 300 are internal to the device.

In the illustrated example, system 300 includes touch sensor 302, touchsensor array 310, measurement circuits 320 a-n, and a direct current(DC) circuit 360. In one example, touch sensor array 310 corresponds totouch sensor array 106, described above with reference to FIG. 1.

Each measurement circuit 320 a-n is be coupled to one or more electrodesof touch sensor array 310 (e.g., electrodes 210 and/or 220 of touchsensor array 200 of FIG. 2). For example, measurement circuit 320 a maybe coupled to electrode 220 a of touch sensor array 200, measurementcircuit 320 b may be coupled to electrode 220 b of touch sensor array200, measurement circuit 320 c may be coupled to electrode 220 c oftouch sensor array 200, and the like. Measurement circuits 320 a-n areconfigured to sense charges flowing into electrodes 210 and/or 220. Inone embodiment, system 300 includes a drive circuit that transmits adrive signal, such as a voltage signal, to one or more electrodes oftouch sensor 310.

In one embodiment, system 300 performs self-capacitance sensing in idlepower mode. In certain embodiments, measurement circuits 320 a-n mayinclude one or more drive circuits. During self-capacitance sensing, theone or more drive circuits of measurement circuits 320 a-n may apply asignal (e.g., a voltage signal) to each respective electrode to whicheach measurement circuit 320 a-n is coupled (e.g., electrodes 220 a-i oftouch sensor array 200) such that the measurement circuits 320 a-n driveand sense the electrodes. The electrodes may be driven one after another(i.e., sequentially) or at substantially the same time (i.e.,simultaneously). In some embodiments, the electrodes are driven andsensed at the same time. In certain embodiments, in the idle power modethe electrodes in one direction (e.g., electrodes 220 a-i of touchsensor array 200) are driven and sensed to reduce power consumption ofsystem 300. It should be understood, however, that the presentdisclosure contemplates driving and sensing electrodes in bothdirections (e.g., the x-direction and y-direction) in the idle powermode.

In one embodiment, in response to detecting some activity (e.g., apotential touch) on touch sensor 302, system 300 transitions fromself-capacitance sensing to mutual-capacitance sensing to measurespatial information (e.g., a location of one or more touches and/or thenumber of touches) and/or touch classification information (e.g.,whether the nature of the touch is a finger, glove, or stylus). Duringmutual-capacitance sensing, each drive electrode (e.g., electrodes 210a-q of touch sensor array 200) may be stimulated, and measurementcircuits 320 a-n may measure each sense electrode (e.g., electrodes 220a-i of touch sensor array 200). Measurements may include charges presenton the sense electrodes and/or changes in the sense electrodes (e.g.,changes in capacitance, voltage, current, charge, or any other suitablemeasurement indicating the capacitance at a capacitive node, such as achange in capacitance.)

System 300 may then transition back to self-capacitance sensing toconserve power. This transition may be triggered by one or more events(e.g., system 300 determines that no activity has occurred on touchsensor 302 within a pre-determined amount of time, system 300 isconfigured for mutual-capacitance sensing for a pre-determined amount oftime, or system 300 determines one or more measurements). In oneembodiment, measurement circuits 320 a-n may be remapped to driveelectrodes (e.g., electrodes 210 a-q) or self-capacitance sensing. As anexample, measurement circuits 320 a-n that are respectively coupled toelectrodes 220 a-i of touch sensor array 200 during mutual-capacitancesensing may be decoupled (e.g., electrically disconnected) fromelectrodes 220 a-i and coupled (e.g., electrically connected) toelectrodes 210 a-q of touch sensor array 200 when system 300 transitionsto self-capacitance sensing to perform sensing of electrodes 210 a-q.

Each signal measured from a particular electrode receiving a drivesignal may include both a touch capacitance and a parasitic capacitance,Cp (e.g., Cp₀₋₃ of FIG. 3). The parasitic capacitance may include thecapacitance of the tracks in the silicon or tracks on the printedcircuit board (PCB). As an example, the capacitance provided by anobject providing the touch or proximity input may add 5-10% of thecapacitance sensed at the particular electrode.

In the illustrated embodiment of FIG. 3, measurement circuit 320 aincludes an amplifier 324 a, an integrator 326 a, and an ADC 328 a. Incertain embodiments, amplifier 324 a is a current input amplifier withan associated current gain Ai. In the illustrated embodiment of FIG. 3,amplifier 324 a receives an incoming current i_(in) from an electrode(e.g., electrode 220 a) and amplifies the incoming current i_(in) toprovide output current i_(in)*A_(i) that is transmitted to integrator326 a. Integrator 326 a integrates the output current from amplifier 324a to generate a voltage V_(in) that is proportional to the outputcurrent. Output voltage V_(in) from integrator 326 a is transmitted toADC 328 a, wherein ADC 328 a digitizes output voltage V_(in).Measurement circuits 320 b-n of FIG. 3 are analogous to measurementcircuit 320 a. As an example, measurement circuit 320 b includes anamplifier 324 b, an integrator 326 b, and an ADC 328 b, whereinamplifier 324 b receives an incoming current i_(in) from an electrode(e.g., electrode 220 b). The total current consumption for eachmeasurement circuit 320 a-n (i.e., each slice) may be represented by thefollowing equation:

I _(slice) =I _(Ai) *I _(int) *I _(ADC)   [Equation 1]

wherein:

I_(slice)=current consumption for each measurement circuit (e.g.,measurement circuits 320 a-n);

I_(Ai)=current consumption for each amplifier (e.g., amplifiers 324a-n);

I_(int)=current consumption for each integrator (e.g., integrators 326a-n); and

I_(ADC)=current consumption for each ADC (e.g., ADC 328 a-n).

Although this disclosure describes particular measurement circuits 320a-n having particular implementations with particular components, thisdisclosure contemplates measurement circuits having otherimplementations with other components. For example, measurement circuits320 a-n may include additional components not illustrated in FIG. 3. Asanother example, the components of measurement circuits 320 a-n may beconfigured in a different order than the order illustrated in FIG. 3.

In the illustrated embodiment of FIG. 3, system 300 providesdifferential sensing to remove pedestal (i.e., offset) capacitance fromthe electrode lines during self-capacitance implementation. For example,a differential connection 340 may connect measurement circuit 320 a tomeasurement circuit 320 b such that currents are subtracted between thetwo measurement circuits. A drawback of differential sensing is that theDC level of the measurement is lost. To recover this lost information, asmall part of the input current i_(in)*A_(DC) of each measurementcircuit 320 a-n is sent to an additional measurement circuit, DC circuit360. For example, amplifier 324 a of measurement circuit 320 a may beconfigured to generate dual outputs. Amplifier 324 a may output a firstoutput signal i_(in)*A_(i) that is transmitted to and received byintegrator 326 a and a second output signal i_(in)*A_(DC) that istransmitted to and received by DC circuit 360. In one embodiment, DCcircuit 360 integrates the sum of the current coming from measurementcircuits 320 a-n to recreate the DC level information.

In one embodiment, DC circuit 360 is a monitoring circuit that includesan amplifier 364, an integrator 366, and an ADC 368. DC circuit 360 maybe coupled to measurement circuits 320 a-n. For example, amplifier 364 aof DC circuit 360 may be coupled to amplifiers 324 a-n of measurementcircuits 320 a-n. In certain embodiments, amplifier 364 is a currentamplifier with an associated current gain Ai. In the illustratedembodiment of FIG. 3, DC circuit 360 receives signals from each ofmeasurement circuits 320 a-n and generates an output signal that isproportional to the sum of the signals received from measurementcircuits 320 a-n. For example, amplifier 364 of DC circuit 360 mayreceive an incoming current i_(in)*A_(DC) from each of measurementcircuits 320 a-n within a pre-determined amount of time, resulting in anincoming current of Σi_(in)*A_(DC). Amplifier 364 of DC circuit 360 thenamplifies incoming current Σi_(in)*A_(DC) to provide output currenti_(in)*A_(i) that is transmitted to integrator 366. Integrator 366integrates the output current from amplifier 366 to generate a voltageV_(in) that is proportional to output current i_(in)*A_(i). Outputvoltage V_(in) from integrator 366 is transmitted to ADC 368, whereinADC 368 digitizes output voltage V_(in). This digitized output valueindicates whether some activity has occurred on the touch sensor.

Although this disclosure describes a particular DC circuit 360 havingparticular implementations with particular components, this disclosurecontemplates any monitoring circuit having other implementations withother components. For example, DC circuit 360 may include additionalcomponents not illustrated in FIG. 3. As another example, the componentsof DC circuit 360 may be configured in a different order than the orderillustrated in FIG. 3.

In the illustrated example embodiment of FIG. 3, amplifiers 324 a-n ofmeasurement circuits 320 a-n are activated during idle consumption mode,wherein integrators 326 a-n and ADCs 328 a-n are deactivated to reducethe power consumption of operating system 300 during idle sensing.Because ADCs 328 a-n of measurement circuits 320 a-n are deactivated,system 300 does not receive values from ADCs 328 a-n. DC circuit 360 isactivated during idle consumption mode such that system 300 receives onevalue from ADC 368 of DC slice 360. This value may represent the sum ofall signals received from electrodes 220 a-i of touch sensor array 200.Since spatial information is not required, sensing of electrodes 210 a-qis not required. For example, if a finger is approaching touch sensor310, the value from ADC 368 may change. The detection of some activity(e.g., the approaching finger) may activate the full system such thatregular touch sensing (e.g., touch location, number of touches, and/ornature of the touch) is performed.

The value received from ADC 368 indicates whether touch sensor 310 hasdetected some activity. For example, a value above a certain thresholdmay indicate a presence of a touch input. Once some activity has beendetected, the full system may be activated so that system 300 canmeasure spatial information and touch classification information. Asjust one example, integrators 326 a-n and ADCs 328 a-n are activatedsuch that system 300 receives values from ADCs 328 a-n of measurementcircuits 320 a-n as well as a value from ADC 368 of DC circuit 360. Inone embodiment, system 300 transitions from self-capacitance sensing tomutual-capacitance sensing upon detecting some activity from touchsensor 310.

Current consumption of system 300 in idle consumption mode may be lessthan ten percent of current consumption of system 300 when system 300 isfully activated. In just one example embodiment, the total currentconsumption of system 300 during idle consumption mode with integrators326 a-n and ADCs 328 a-n deactivated is one-twelfth of the total currentconsumption during idle consumption mode with integrators 326 a-n andADCs 328 a-n activated. Equation 2 illustrates an example equation forcomputing total current consumption during idle consumption mode whenamplifiers 326 a-n, integrators 326 a-n, and ADCs 328 a-n of measurementcircuits 320 a-n are activated:

I _(tot)=(I _(slice) *n _(y) +I _(DCslice))*(1+ceiling n _(x) /n_(y)))*t _(sample) *n _(avg) *f _(refresh)   [Equation 2]

wherein:

L_(tot)=total current consumption in idle mode;

I_(slice)=current consumption for each measurement circuit (e.g.,measurement circuits 320 a-n);

n_(y)=number of Y electrodes (e.g., number of electrode lines 220 a-220i);

n_(x)=number of X electrodes (e.g., number of electrode lines 210 a-210q);

I_(DCslice)=current consumption for a monitoring circuit (e.g., DCcircuit 360);

t_(sample)=sensing time for one sample;

n_(avg)=average number of samples per measurement used for noiseaveraging; and

f_(refresh)=touch sensor scan frequency.

As just one example calculation for Equation 2:

I _(tot)=((1*10⁻³*9+1*10⁻³)*(1+ceiling 17/9))*(15*10⁻⁶)*64*20

I_(tot)=576 microamperes (μA)

wherein:

I_(slice)=1 milliampere (mA) (1/3 for amplifier, 1/3 for integrator, and1/3 for ADC);

n_(y)=9;

n_(x)=17;

I_(DCslice)=1 mA;

t_(sample)=15 microseconds (μs);

n_(avg)=64; and

f_(refresh)=20 hertz (Hz).

Equation 3 illustrates an example equation for computing total currentconsumption during idle consumption mode when system 300 has beenmodified to reduce power consumption such that amplifiers 326 a-n ofmeasurement circuits 320 a-n are activated and integrators 326 a-n andADCs 328 a-n of measurement circuits 320 a-n are deactivated:

I _(tot) _(_) _(idle)=(I _(Ailow) *n _(y) +I _(DC))*t _(sample) *n_(avg) *f _(refresh)   [Equation 3]

wherein:

I_(tot) _(_) _(idle)=total current consumption in idle mode; and

I_(Ailow)=amplifier current consumption for the amplifier in idle mode.

As just one example calculation for Equation 3:

I _(tot) _(_) _(idle)=(0.166*10⁻³*9+1*10⁻³)*15*10⁻⁶*64*20

I_(tot) _(_) _(idle)=48 μA

wherein:

I_(Ailow)=0.166 mA (50% of ⅓ amplifier is required);

n_(y)=9;

I_(DC)=1 mA;

t_(sample)=15 μs;

n_(avg)=64; and

f_(refresh)=20 Hz.

As shown in the above example calculations for Equations 2 and 3, totalcurrent consumption I_(tot) during idle consumption mode whenintegrators 326 a-n and ADCs 328 a-n of system 300 are activated isapproximately 576 μA, whereas total current consumption I_(tot) _(_)_(idle) of modified system 300 when integrators 326 a-n and ADCs 328 a-nare deactivated is approximately 48 μA, which is one-twelfth of theconsumption of the fully activated system. Whereas original system 300with activated integrators 326 a-n and ADCs 328 a-n may measure spatialinformation (e.g., x and y coordinates of a touch position), modifiedsystem 300 with deactivated integrators 326 a-n and ADCs 328 a-n may bemeasure some activity rather than a specific touch position. In certainembodiments, modified system 300 may sense the electrodes of system 300at one time as one capacitance. In both the original system and themodified system of the above examples, amplifier 364, integrator 366,and ADC 368 of DC circuit 360 are fully activated. In the modifiedsystem, the amplifier consumes approximately fifty percent of itsmaximum current consumption, which reduces the current consumption ofthe amplifier from 0.333 mA for the original system to 0.166 mA for themodified system. In some embodiments, touch sensor scan frequencyf_(refresh) can be reduced in the modified system as compared to theoriginal system.

Equations 1 through 3 are provided as examples only. The presentdisclosure contemplates equations including additional or fewervariables and other techniques for determining current consumption,according to particular needs.

FIG. 4 illustrates an example method 400 for configuring a power modefor a touch sensor, according to an embodiment of the presentdisclosure. Method 400 starts at step 405. At step 410, a controller(e.g., controller 108 of FIG. 1) respectively couples measurementcircuits (e.g., measurement circuits 320 a-n) to electrodes (e.g.,electrode lines 220 a-i) of a touch sensor (e.g., touch sensor 310) of adevice. Each measurement circuit may include a first component, a secondcomponent, and a third component. In one embodiment, the first componentis an amplifier (e.g., amplifier 324 a), the second component is anintegrator (e.g., integrator 326 a), and the third component is an ADC(e.g., ADC 328 a). At step 415 of FIG. 4, the controller couples amonitoring circuit to the measurement circuits. In some embodiments, themonitoring circuit is a DC circuit (e.g., DC circuit 360). Themonitoring circuit includes a first component, a second component, and athird component. In one embodiment, the first component of themonitoring circuit is an amplifier (e.g., amplifier 364), the secondcomponent of the monitoring circuit is an integrator (e.g., integrator366), and the third component of the monitoring circuit is an ADC (e.g.,ADC 368).

At step 420 of method 400, the controller activates the first componentof each of the measurement circuits. As an example, controller 108 mayactivate amplifiers 324 a-n such that amplifiers 324 a-n are powered onin a first power mode. In one embodiment, the activated amplifiersconsume approximately fifty percent of the amplifier's maximum currentconsumption. At step 425 of method 400, the controller deactivates theintegrators and the ADCs of each measurement circuit. For instance,controller 108 may power off integrators 326 a-n and ADCs 328 a-n in thefirst power mode. At step 430, the controller activates the threecomponents of the monitoring circuit. For example, controller 108 ofFIG. 1 may activate amplifier 364, integrator 366, and ADC 368 of DCcircuit 360.

The monitoring circuit of method 400 may perform one or more operationsin the first power mode. As illustrated in step 435, the monitoringcircuit may receive signals from each of the measurement circuits. Inone embodiment, DC circuit 360 receives a signal from each integrator324 a-n of measurement circuits 320 a-n. At step 440 of method 400, themonitoring circuit generates an output signal that is proportional to asum of the signals received from the measurement circuits. For example,ADC 368 of DC circuit 360 may digitize a value representative of anoutput voltage from integrator 366, wherein the value is proportional tothe sum of the current consumption of each measurement circuit.

Method 400 then moves to step 445, where the controller determineswhether the value of the generated output signal indicates an activityhas occurred on the touch sensor. For example, the controller maydetermine whether the value is above a pre-determined threshold. If thevalue of the generated output signal fails to indicate an activity hasoccurred on the touch sensor (e.g., the value is below a pre-determinedthreshold), method 400 moves back to step 435. If the value indicatesactivity has occurred on the touch sensor (e.g., the value is at orabove a pre-determined threshold), method 400 proceeds to step 450,where all three components of the measurement circuits are activated ina second power mode. For example, controller 180 may activate amplifiers324 a-n, integrators 326 a-n, and ADCs 328 a-n of measurement circuits320 a-n such that spatial and touch classification information can bedetermined. At step 455 of method 400, the controller determines alocation of a touch. In one embodiment, the controller may additionallyor alternatively determine a number of touches or the nature of thetouches (e.g., a finger, glove, or stylus.) Method 400 ends at step 460.

In certain embodiments, method 400 may transition from second power modeto first power mode. For example, after activating the components ofeach monitoring circuit for the second power mode in step 450, method400 may revert back to step 420, where the amplifier of each measurementcircuit is activated in the first power mode (e.g., fifty percent ofmaximum current consumption) and the integrators and ADCs of eachmeasurement circuit are deactivated in the first power mode. Thistransition from second power mode to first power mode may be triggeredby one or more events, such as a determination by the system that noactivity has occurred on the touch sensor within a pre-determined amountof time.

FIG. 4 illustrates just one example method 400 for configuring a powermode for a touch sensor, and the present disclosure contemplates otherimplementations of the method. For example, one or more of theintegrators or ADCs of the measurement circuits may be activated duringthe first power mode. As another example, the measurement circuits maybe remapped such that they are coupled to different electrodes dependingon whether self-capacitance implementation or mutual-capacitanceimplementation is being used. As still another example, method 400 maytransition from the first power mode to the second power mode based on atime frequency rather than an indication of touch activity.

Although this disclosure describes and illustrates particular steps ofthe methods of FIG. 4 as occurring in a particular order, thisdisclosure contemplates any steps of the methods of FIG. 4 occurring inany order. For example, steps 410 and 415 of FIG. 4 may occursimultaneously. An embodiment may repeat one or more steps of themethods of FIG. 4. Moreover, although this disclosure describes andillustrates an example method for configuring a power mode for a touchsensor including the particular steps of the method of FIG. 4, thisdisclosure contemplates any method for configuring a power mode for atouch sensor including any steps, which may include all, some, or noneof the steps of the method of FIG. 4. Moreover, although this disclosuredescribes and illustrates particular components performing particularsteps of the method of FIG. 4, this disclosure contemplates anycombination of any components performing any steps of the method of FIG.4.

Embodiments of the present disclosure may provide one or more technicaladvantages. An embodiment of the present disclosure conserves power thatwould otherwise be consumed by a device. For example, rather thanconfiguring the device to detect spatial information and/or touchclassification information in idle power mode, an embodiment of thepresent disclosure configures the device to detect limited touchactivity to conserve power. Transitioning touch sensor 102 from a firstpower mode to a second power mode upon detection of some activity mayreduce or eliminate reasons to power one or more components of touchsensor 102 during idle power mode. In one embodiment, the components ofa device collectively consume less power than would otherwise be used topower the device to detect a location of a touch, the number of touches,or the nature of the touch.

Certain embodiments of the present disclosure may include none, some, orall of the above technical advantages. One or more other technicaladvantages may be readily apparent to one skilled in the art from thefigures, descriptions, and claims included herein.

Herein, a computer-readable non-transitory storage medium or media mayinclude one or more semiconductor-based or other integrated circuits(ICs) (such, as for example, field-programmable gate arrays (FPGAs) orapplication-specific ICs (ASICs)), hard disk drives (HDDs), hybrid harddrives (HHDs), optical discs, optical disc drives (ODDS),magneto-optical discs, magneto-optical drives, floppy diskettes, floppydisk drives (FDDs), magnetic tapes, solid-state drives (SSDs),RAM-drives, SECURE DIGITAL cards or drives, any other computer-readablenon-transitory storage media, or any combination of two or more ofthese. A computer-readable non-transitory storage medium may bevolatile, non-volatile, or a combination of volatile and non-volatile.

Herein, “or” is inclusive and not exclusive, unless expressly indicatedotherwise or indicated otherwise by context. Therefore, herein, “A or B”means “A, B, or both,” unless expressly indicated otherwise or indicatedotherwise by context. Moreover, “and” is both joint and several, unlessexpressly indicated otherwise or indicated otherwise by context.Therefore, herein, “A and B” means “A and B, jointly or severally,”unless expressly indicated otherwise or indicated otherwise by context.Additionally, components referred to as being “coupled” includes thecomponents being directly coupled or indirectly coupled.

This disclosure encompasses a myriad of changes, substitutions,variations, alterations, and modifications to the example embodimentsherein that a person having ordinary skill in the art would comprehend.Similarly, where appropriate, the appended claims encompass all changes,substitutions, variations, alterations, and modifications to the exampleembodiments herein that a person having ordinary skill in the art wouldcomprehend. Moreover, reference in the appended claims to an apparatusor system or a component of an apparatus or system being adapted to,arranged to, capable of, configured to, enabled to, operable to, oroperative to perform a particular function encompasses that apparatus,system, component, whether or not it or that particular function isactivated, turned on, or unlocked, as long as that apparatus, system, orcomponent is so adapted, arranged, capable, configured, enabled,operable, or operative.

What is claimed is:
 1. A system, comprising: a touch sensor comprising aplurality of electrodes; a plurality of measurement circuitsrespectively coupled to the plurality of electrodes of the touch sensor,each measurement circuit comprising a first component, a secondcomponent, and a third component, wherein: the first component of eachmeasurement circuit is activated in a first power mode; and the secondcomponent and the third component of each measurement circuit aredeactivated in the first power mode; and a monitoring circuit coupled tothe first component of each measurement circuit, the monitoring circuitcomprising a first component, a second component, and a third component,wherein: the first component, the second component, and the thirdcomponent of the monitoring circuit are activated in the first powermode; and the monitoring circuit is configured to perform operations inthe first power mode comprising: receiving respective signals from theplurality of measurement circuits; and generating an output signal thatis proportional to a sum of the signals received from the plurality ofmeasurement circuits, a value of the generated output signal indicatingwhether activity has occurred on the touch sensor.
 2. The system ofclaim 1, further comprising a differential connection between a firstmeasurement circuit and a second measurement circuit of the plurality ofmeasurement circuits, wherein the differential connection is configuredto subtract currents between the first measurement circuit and thesecond measurement.
 3. The system of claim 1, wherein: the firstcomponent, the second component, and the third component of eachmeasurement circuit are activated in a second power mode; the firstcomponent, the second component, and the third component of themonitoring circuit are activated in the second power mode; and currentconsumption of the system in the first power mode is less than tenpercent of current consumption of the system in the second power mode.4. The system of claim 1, wherein: the first component of eachmeasurement circuit is a current input amplifier; the second componentof each measurement circuit is an integrator; and the third component ofeach measurement circuit is an analog-to-digital converter (“ADC”). 5.The system of claim 1, wherein the system is configured to: performself-capacitance scanning in the first power mode; transition, when thevalue of the generated output signal indicates activity has occurred onthe touch sensor, from the first power mode to a second power mode byactivating the second component and the third component of eachmeasurement circuit; perform mutual-capacitance scanning in the secondpower mode; and determine a touch location and a number of touches inthe second power mode.
 6. The system of claim 1, wherein the monitoringcircuit is configured to receive the respective signals from theplurality of measurement circuits from a current input amplifier of eachof the measurement circuits, each signal comprising an unamplifieddirect current level from the respective electrode to which themeasurement circuit is coupled.
 7. The system of claim 1, wherein thefirst component of each measurement circuit consumes approximately fiftypercent of its maximum current consumption in the first power mode. 8.The system of claim 1, wherein: the first component of the monitoringcircuit is a current input amplifier; the second component of themonitoring circuit is an integrator; and the third component of themonitoring circuit is an ADC.
 9. A non-transitory computer-readablemedium embodying logic, the logic configured to, when executed by one ormore processors, cause the one or more processors to perform operationscomprising: respectively coupling a plurality of measurement circuits toa plurality of electrodes of a touch sensor of a device, eachmeasurement circuit comprising a first component, a second component,and a third component; coupling a monitoring circuit to first componentof each measurement circuit, the monitoring circuit comprising a firstcomponent, a second component, and a third component; activating thefirst component of each measurement circuit in a first power mode;deactivating the second component and the third component of eachmeasurement circuit in the first power mode; activating the firstcomponent, the second component, and the third component of themonitoring circuit in the first power mode; and performing operations inthe first power mode comprising: receiving, by the monitoring circuit,respective signals from the plurality of measurement circuits; andgenerating an output signal that is proportional to a sum of the signalsreceived from the plurality of measurement circuits, a value of thegenerated output signal indicating whether activity has occurred on thetouch sensor.
 10. The non-transitory computer-readable medium of claim9, wherein the operations further comprise: connecting, by adifferential connection, a first measurement circuit of the plurality ofmeasurement circuits to a second measurement circuit of the plurality ofmeasurement circuits; and subtracting, by the differential connection,currents between the first measurement circuit and the secondmeasurement circuit.
 11. The non-transitory computer-readable medium ofclaim 9, wherein the operations further comprise: activating the firstcomponent, the second component, and the third component of eachmeasurement circuit in a second power mode; and activating the firstcomponent, the second component, and the third component of themonitoring circuit in the second power mode; wherein current consumptionof the system in the first power mode is less than ten percent ofcurrent consumption of the system in the second power mode.
 12. Thenon-transitory computer-readable medium of claim 9, wherein: the firstcomponent of each measurement circuit is a current input amplifier; thesecond component of each measurement circuit is an integrator; and thethird component of each measurement circuit is an analog-to-digitalconverter (“ADC”).
 13. The non-transitory computer-readable medium ofclaim 9, wherein the operations further comprise: performingself-capacitance scanning when the system is in the first power mode;transitioning from the first power mode to a second power mode when thevalue of the generated output signal indicates activity has occurred onthe touch sensor by activating the second component and the thirdcomponent of each measurement circuit; performing mutual-capacitancescanning when the system is in the second power mode; and measuringspatial information and touch classification information in the secondpower mode.
 14. The non-transitory computer-readable medium of claim 9,wherein the respective signals are received from the plurality ofmeasurement circuits from a current input amplifier of each of themeasurement circuits, each signal comprising an unamplified directcurrent level from the respective electrode to which the measurementcircuit is coupled.
 15. The non-transitory computer-readable medium ofclaim 9, wherein the first component of each measurement circuitconsumes approximately fifty percent of its maximum current consumptionin the first power mode.
 16. The non-transitory computer-readable mediumof claim 9, wherein: the first component of the monitoring circuit is acurrent input amplifier; the second component of the monitoring circuitis an integrator; and the third component of the monitoring circuit isan ADC.
 17. A method, comprising: respectively coupling a plurality ofmeasurement circuits to a plurality of electrodes of a touch sensor of adevice, each measurement circuit comprising a first component, a secondcomponent, and a third component; coupling a monitoring circuit to thefirst component of each measurement circuit, the monitoring circuitcomprising a first component, a second component, and a third component;activating the first component of each measurement circuit in a firstpower mode; deactivating the second component and the third component ofeach measurement circuit in the first power mode; activating the firstcomponent, the second component, and the third component of themonitoring circuit in the first power mode; and performing operations inthe first power mode comprising: receiving, by the monitoring circuit,respective signals from the plurality of measurement circuits; andgenerating an output signal that is proportional to a sum of the signalsreceived from the plurality of measurement circuits, a value of thegenerated output signal indicating whether activity has occurred on thetouch sensor.
 18. The method of claim 17, further comprising:connecting, by a differential connection, a first measurement circuit ofthe plurality of measurement circuits to a second measurement circuit ofthe plurality of measurement circuits; and subtracting, by thedifferential connection, currents between the first measurement circuitand the second measurement circuit.
 19. The method of claim 17, furthercomprising: activating the first component, the second component, andthe third component of each measurement circuit in a second power mode;and activating the first component, the second component, and the thirdcomponent of the monitoring circuit in the second power mode; whereincurrent consumption of the system in the first power mode is less thanten percent of current consumption of the system in the second powermode.
 20. The method of claim 17, wherein: the first component of eachmeasurement circuit is a current input amplifier; the second componentof each measurement circuit is an integrator; and the third component ofeach measurement circuit is an analog-to-digital converter (“ADC”).